What does override mean?

The override is used when you want to write your own method to replace an existing one in a parent class. It's used commonly when you're working with UIViewControllers, because view controllers already come with lots of methods like viewDidLoad() and viewWillAppear(). When you want to override these default methods, you need to specify this with the override keyword.

Now, you might be wondering why the override keyword is even needed, but it's really about ensuring your code is safe – if you write a method and accidentally name it the same as something that already exists, Xcode will simply refuse to build your app until you add in the override keyword. Similarly, if you use override on a method that doesn't override something that already exists, Xcode will refuse to build.